The addition of a hydrogen donor to a residual oil prior to a coking or visbreaking operation is known to decrease markedly the amount of coke made and to improve the quality of the overhead product by increasing the yield of distillate. Typical hydrogen donors are tetralin from the hydrogenation of naphthalene, alkyl substituted tetralin, hydrogenated anthracenes, phenanthrenes, pyrenes, and the hydrogenated derivatives of other condensed ring aromatics. In such processes the hydrogen donor functions to supply hydrogen to thermally cracked hydrocarbon fragments thereby reducing coke formation and providing a superior cracked product. The actual hydrogen donation can be carried out on the resid in a heat-soak drum before the coking or visbreaking operation or it can take place during the coking or visbreaking operation. One problem with hydrogen donation in using a heat soak drum is the length of time it takes for the hydrogen to be transferred to the resid.
A primary object of this invention is to provide a means of accelerating the transfer of hydrogen from the donor to the resid during the heat soaking operation prior to a visbreaking or coking operation.